Optical unit and projector therewith

ABSTRACT

In an optical unit, illumination light is directed to a plurality of digital micromirror devices that produce projection light by modulating the illumination light on an image display surface according to an image signal. The optical unit emits the projection light produced by the digital micromirror devices. The optical unit includes: a reflector having an illumination light reflecting face on which the illumination light is reflected; and a prism unit composed of a plurality of first prisms. The reflected illumination light enters the prism unit via a first face of a most emergence-side first prism among the first prisms and the projection light exits via the first face.

CROSS REFERENCE TO RELATED APPLICATIONS

The entire disclosure of Japanese Patent Application No. 2017-131249,filed on Jul. 4, 2017, is incorporated herein by reference in itsentirety.

BACKGROUND 1. Technical Field

The present invention relates to an optical unit that receivesillumination light and emits projection light reflected from a digitalmicromirror device, and relates also to a projector provided with suchan optical unit.

2. Description of the Related Art

A projector incorporating a conventional optical unit is disclosed inPatent Document 1 identified below. This projector includes a lightsource, an optical unit, a plurality of digital micromirror devices, anda projection lens. The optical unit includes a total reflection lightseparation prism and a cross dichroic prism. From the projection side(emergence side) toward the digital micromirror devices, the totalreflection light separation prism and the cross dichroic prism arearranged in this order.

The digital micromirror device is a reflective image display element ina rectangular shape as seen in a plan view, and has an image displaysurface composed of a plurality of minute micromirrors. The digitalmicromirror device forms an image by producing projection light throughintensity modulation on illumination light through ON/OFF control of theinclination of the faces of the micromirrors. Each micromirror pivotsabout a pivot axis of the digital micromirror device so that it hasdifferent angles of inclination in an ON state and in an OFF state.

The total reflection light separation prism is composed of two prisms;one prism has an emergence face, and the other prism has an entranceface and a total reflection face as well as a protruding portion thatprotrudes toward the emergence face in the emergence direction. Part ofthe total reflection face is provided in the protruding portion, andwhite illumination light that has entered the total reflection lightseparation prism via the entrance face is totally reflected toward thecross dichroic prism. The emergence face is disposed to face theprojection lens, and the projection light produce by the digitalmicromirror devices is emitted toward the projection lens.

The cross dichroic prism has two mutually perpendicular dichroic coatfaces; it separates the white illumination light totally reflected fromthe total reflection face in the total reflection light separation prisminto a red, a green, and a blue component, and directs these to thedigital micromirror devices respectively. The cross dichroic prism alsointegrates together red, green, and blue ON-light (projection light)reflected from micromirrors in the ON state in the digital micromirrordevices, and emits the color-integrated ON-light toward the totalreflection light separation prism. The most emergence face-side face ofthe cross dichroic prism is parallel to the emergence face, and isperpendicular to the optical axis of the color-integrated ON-light.

In the projector structured as descried above, the white illuminationlight emitted from the light source and entered the total reflectionlight separation prism is totally reflected on the total reflection facein it, and then exits from the total reflection light separation prismto enter the cross dichroic prism. The illumination light entered thecross dichroic prism undergoes color separation, so that the red, green,and blue components of the illumination light are emitted to thedifferent digital micromirror devices respectively.

The red, green, and blue ON-light reflected from micromirrors in the ONstate in the digital micromirror devices enters the cross dichroic prismto undergo color integration, and is emitted toward the total reflectionlight separation prism. The color-integrated ON-light passes through thetotal reflection face in the total reflection light separation prism,and then exits via the emergence face, so that it then passes throughthe projection lens. Thus, a color image is projected.

Patent Document 1: Japanese Patent Application published as No.2007-25287 (pages 5 and 6; FIGS. 1 and 3).

In projectors, it is common to move the projection lens in the up-downor left-right direction to change the projection position of theprojected image. That is, in projectors, it is common to shift theprojection lens up and down or left and rightward. Inconveniently, inthe conventional optical unit described above, the total reflectionlight separation prism has a protruding portion that protrudes in theemergence direction, and the projection lens is disposed to the side ofthe protruding portion, near it. Thus, the movement of the projectionlens in the left-right direction is restricted, and the left-right shiftamount of the projection lens (that is, the distance over which it canmove left and rightward) is reduced. In a case where the protrudingportion of the total reflection light separation prism is disposed underthe projection lens, near it, the movement of the projection lens in theup-down direction is restricted, and the up-down shift amount of theprojection lens (that is, the distance over which it can move up anddown) is reduced. This, disadvantageously, results in diminishedusability of the optical unit and the projector.

On the other hand, by moving the protruding portion (total reflectionface) of the total reflection light separation prism along the mostemergence-side face of the cross dichroic prism in the direction awayfrom the projection lens, it is possible to increase the left-right orup-down shift amount of the projection lens. Inconveniently, in thiscase, of all the rays of the illumination light traveling toward thetotal reflection light separation prism, some cross dichroic prism-siderays may not reach the entrance face. Such cross dichroic prism-siderays of the illumination light can be made to reach the entrance face bychanging the angle of incidence of the illumination light with respectto the entrance face, but then part of the illumination light is nottotally reflected on but transmitted through the total reflection face.This reduces the amount of illumination light that is totally reflectedon the total reflection face in the total reflection light separationprism, and reduces the amount of illumination light that strikes thedigital micromirror devices, disadvantageously resulting in a drop inthe amount of projection light.

SUMMARY

One or more embodiments of the present invention provide an optical unitthat offers enhanced usability while preventing a drop in the amount ofprojection light, and to provide a projector provided with such anoptical unit.

According to one or more embodiments of the present invention, anoptical unit in which illumination light is directed to a plurality ofdigital micromirror devices that produce projection light by modulatingthe illumination light on an image display surface according to an imagesignal so that the optical unit emits, by transmitting, the projectionlight produced by the plurality of digital micromirror devices includes:a reflecting member having an illumination light reflecting face onwhich the illumination light is reflected; and a prism unit composed ofa plurality of first prisms, the illumination light reflected from theillumination light reflecting face entering via a first face of a mostemergence-side first prism, the projection light exiting via the firstface. The reflecting member is close to the first face and is disposedso as to protrude from the first face in the projection light exitingdirection. The optical axis of the illumination light striking, asincident light, the illumination light reflecting face and the opticalaxis of the projection light on the first face are disposed on the sameplane which is the optical axis plane. A first component vector that isobtained, when a first, outward, normal vector to the first face isprojected onto the optical axis plane, by it being projected to bedisposed on the same side as the optical axis of the incident light withrespect to the optical axis of the projection light points in such adirection that, the farther away from the first face, the farther awayfrom the optical axis of the projection light leaving the first face.

According to one or more embodiments of the present invention, aprojector includes: an optical unit as described above; a light source;an illumination optical system that emits illumination light toward thereflecting member in the optical unit; and a projection optical systemthat projects onto a screen, on an enlarged scale, the image displayedon the digital micromirror devices fitted to the fitting portions.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features provided by one or more embodiments of theinvention will become more fully understood from the detaileddescription given hereinbelow and the appended drawings which are givenby way of illustration only, and thus are not intended as a definitionof the limits of the present invention:

FIG. 1 is an outline configuration diagram of a projector provided withan optical unit according to one or more embodiments of the presentinvention;

FIG. 2 is a perspective view of the optical unit according to one ormore embodiments of the present invention;

FIG. 3 is an exploded perspective view of the optical unit according toone or more embodiments of the present invention;

FIG. 4 is a top view of the optical unit according to one or moreembodiments of the present invention;

FIG. 5 is a side view of the optical unit according to one or moreembodiments of the present invention;

FIG. 6 is a side sectional view of the optical unit according to one ormore embodiments of the present invention;

FIG. 7 is a perspective view showing a reference state, an ON state, andan OFF state of a micromirror in a digital micromirror device in theoptical unit according to one or more embodiments of the presentinvention;

FIG. 8 is a perspective view illustrating the operation of a digitalmicromirror device in the optical unit according to one or moreembodiments of the present invention;

FIG. 9 is a diagram schematically showing illumination light strikingmicromirrors in a digital micromirror device, ON-light reflected frommicromirrors in the ON state, and OFF-light reflected from micromirrorsin the OFF state in the optical unit according to one or moreembodiments of the present invention;

FIG. 10 is a side sectional view of an optical unit of a comparativeexample;

FIG. 11 is a perspective view of an optical unit according to one ormore embodiments of the present invention;

FIG. 12 is a top view of the optical unit according to one or moreembodiments of the present invention;

FIG. 13 is a side view of the optical unit according to one or moreembodiments of the present invention;

FIG. 14 is a side sectional view of the optical unit according to one ormore embodiments of the present invention;

FIG. 15 is a perspective view of an optical unit according to one ormore embodiments of the present invention;

FIG. 16 is a top view of the optical unit according to one or moreembodiments of the present invention;

FIG. 17 is a side view of the optical unit according to one or moreembodiments of the present invention;

FIG. 18 is a side sectional view of the optical unit according to one ormore embodiments of the present invention;

FIG. 19 is a perspective view of an optical unit according to one ormore embodiments of the present invention;

FIG. 20 is a side view of the optical unit according to one or moreembodiments of the present invention;

FIG. 21 is a side sectional view of the optical unit according to one ormore embodiments of the present invention;

FIG. 22 is a perspective view of an optical unit according to one ormore embodiments of the present invention;

FIG. 23 is a top view of the optical unit according to one or moreembodiments of the present invention;

FIG. 24 is a side view of the optical unit according to one or moreembodiments of the present invention;

FIG. 25 is a side sectional view of the optical unit according to one ormore embodiments of the present invention;

FIG. 26 is a perspective view illustrating the operation of a digitalmicromirror device in the optical unit according to one or moreembodiments of the present invention;

FIG. 27 is a perspective view of an optical unit according to one ormore embodiments of the present invention;

FIG. 28 is a top view of the optical unit according to one or moreembodiments of the present invention; and

FIG. 29 is a side sectional view of the optical unit according to one ormore embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings. However, the scope of the invention is notlimited to the disclosed embodiments.

Hereinafter, with reference to the accompanying drawings, one or moreembodiments of the present invention will be described. FIG. 1 is anoutline configuration diagram of a projector provided with an opticalunit according to one or more embodiments. A three-chip (three-panel)projector PJ includes a light source 1, an illumination optical system2, an optical unit PU, digital micromirror devices DP1, DP2, and DP3(see also FIG. 4), a projection optical system LN, an actuator 4, and acontroller 3.

The light source 1 comprises, for example, an LED, and emits whitelight. The illumination optical system 2 includes an integrator, a relaylens group, a reflecting mirror, and the like (of which none isillustrated). The illumination optical system 2 converges the lightemitted from the light source 1 to emit it, as illumination light L1,toward the optical unit PU.

FIG. 2 is a perspective view of the optical unit PU. In FIG. 2, the Xdirection is a direction along the thickness of a prism unit P2. The Zdirection is a direction along the optical axis AX2 of projection lightreflected from the digital micromirror device DP2. The Y direction is adirection perpendicular to both the X and Z directions. The optical unitPU includes one internal total reflection prism P1 (reflecting member orreflector), one color-separating/integrating prism unit P2 (prism unit),one projection-side prism P3 (second prism), and three OFF-lightseparating prisms P4 (third prisms). The color-separating/integratingprism unit P2 includes a prism P21 (first prism), a prism P22 (firstprism), and a prism P23 (first prism).

As the material for the internal total reflection prism P1, the prismsP21 to P23 in the color-separating/integrating prism unit P2, theprojection-side prism P3, and the OFF-light separating prisms P4, forexample, glass can be used. In one or more the embodiments underdiscussion, the internal total reflection prism P1, the prisms P21, P22,and P23, the projection-side prism P3, and the OFF-light separatingprisms P4 are formed of glass with the same index of refraction.

The optical unit PU is supported by a support member (unillustrated)inside the projector PJ. The support member is disposed to make contactwith the top and bottom faces of the optical unit PU as seen in FIG. 2,and thus holds the optical unit PU from above and below. The opticalunit PU has three fitting portions (unillustrated) for the fitting ofthe digital micromirror devices DP1, DP2, and DP3 each in asubstantially rectangular shape as seen in a plan view. The fittingportions are, for example, metal frames, and are provided to correspondto the prisms P21, P22, and P23 respectively.

As will be described later, the optical unit PU receives theillumination light L1 via the internal total reflection prism P1, andemits projection light (ON-light, which will be described later)reflected from the digital micromirror devices DP1, DP2, and DP3 towardthe projection optical system LN. In the following description, thedigital micromirror devices DP1 to DP3 are occasionally referred tocollectively as “digital micromirror devices DP”. The optical unit PUand the digital micromirror devices DP will be described in detaillater.

The projection optical system LN includes lenses 51 and 52 (see FIG. 5)and the like, and projects the image displayed on the digitalmicromirror devices DP onto a screen SC on an enlarged scale. Theactuator 4 moves the lenses 51 and 52 along the optical axis AX toachieve, for example, zooming and focusing. The actuator 4 also movesthe lenses 51 and 52 in the up-down direction as seen in FIGS. 1 and 5to permit the position (projection position) of the projected image tobe changed in the up-down direction. That is, the actuator 4 and theprojection optical system LN shift the projected image up and down. Thecontroller 3 includes a CPU, and controls the entire projector PJ.

FIGS. 3 to 6 are an exploded perspective view, a top view, a side view,and a side sectional view, respectively, of the optical unit PU. FIG. 6is a view along a sectional plane that passes through the digitalmicromirror device DP2 and that includes the optical axis AX2 of theON-light L2 (projection light) reflected from the digital micromirrordevice DP2. The optical axis AX2 of the ON-light L2 reflected from thedigital micromirror device DP2 coincides with the line normal to, andpassing through the center of, the digital micromirror device DP2. Theoptical axis A1 of the illumination light L1 coincides with the opticalpath of the ray of the illumination light L1 that strikes the center ofthe digital micromirror devices DP.

The color-separating/integrating prism unit P2 is disposed between thedigital micromirror device DP2 and the internal total reflection prismP1. On the projection side (emergence side) of thecolor-separating/integrating prism unit P2, the projection-side prismP3, which is wedge-shaped, is disposed.

Between the digital micromirror device DP1 and thecolor-separating/integrating prism unit P2, between the digitalmicromirror device DP2 and the color-separating/integrating prism unitP2, and between the digital micromirror device DP3 and thecolor-separating/integrating prism unit P2, the OFF-light separatingprisms P4 are disposed respectively. That is, the OFF-light separatingprisms P4 are provided to correspond to the digital micromirror devicesDP respectively.

Between the digital micromirror devices DP and the OFF-light separatingprisms P4, cover glasses CG (see FIG. 6) are provided respectively. InFIGS. 2 to 5, the cover glasses CG are omitted from illustration.

FIG. 7 is a perspective view showing a reference state, an ON state, andan OFF state of a micromirror MR in a digital micromirror device DP.FIG. 8 is a perspective view illustrating the operation of a digitalmicromirror device DP. A digital micromirror device DP has a pluralityof minute micromirrors MR, each substantially square in shape as seen ina plan view, that are disposed in a matrix. The micromirrors MR aremounted on a substrate SB, and the substrate SB is housed in a housing(unillustrated) substantially rectangular in shape.

The reference state of the micromirror MR is indicated by a referenceplane MS1, the ON state of the micromirror MR is indicated by areflective surface MS2, and the OFF state of the micromirror MR isindicated by a reflective surface MS3. The micromirror MR can, from thereference state, incline with respect to a first axis ax1 and then pivotwith respect to a second axis ax2 perpendicular to the first axis ax1.Thus, the digital micromirror device DP has an image display surface DScomposed of a plurality of pixel reflection facets MS, and these pixelreflection facets MS are ON/OFF controlled such that the micromirrors MReach take one of two angle states, namely an image displaying state (ONstate) and an image non-displaying state (OFF state). That is, thedigital micromirror device DP drives the micromirrors MR with respect totwo mutually perpendicular axes to allow each of them to take one of thereference state, the ON state, and the OFF state. Thus, the digitalmicromirror device DP constitutes a reflective image display device thatproduces a desired image through intensity modulation on theillumination light L1. That is, the digital micromirror device DPproduces the projection light through intensity modulation on theillumination light L1.

Since each micromirror MR is driven with respect to two mutuallyperpendicular axes (first and second axes ax1 and ax2), the pixelreflection facet MS of the micromirror MR inclines within differentplanes. In the digital micromirror device DP2 in one or more theembodiments under discussion, a state inclined within the YZ plane isthe ON state, and a state inclined in the XZ plane is the OFF state. Intypical ON/OFF control, when a pixel reflection facet MS is in the ONstate, the illumination light L1 striking the micromirror MR isreflected in the direction normal to the image display surface DS (thatis, normal to the digital micromirror device DP) to become ON-light L2(projection light). On the other hand, when a pixel reflection facet MSis in the OFF state, the illumination light L1 striking the micromirrorMR is reflected at a large angle relative to the direction normal to theimage display surface DS to become OFF-light L3 (unnecessary light).

Thus, as shown in FIG. 9, near the digital micromirror device DP2, eachmicromirror MR reflects the OFF-light L3 in such a direction that theoptical axis AX3 of the OFF-light L3 is increasingly far away from anoptical axis plane AP that includes the optical axis AX2 of the ON-lightL2 and the optical axis AX1 of the illumination light L1. The linenormal to the image display surface DS (the line normal to the digitalmicromirror device DP) is parallel to the optical axis AX2 of theON-light L2 (projection light) near the digital micromirror device DP2.Also near the digital micromirror devices DP1 and DP3, as with thedigital micromirror device DP2, each micromirror MR reflects theOFF-light L3 in such a direction that it is increasingly far away fromthe plane (unillustrated) that includes the optical axes AX1 and AX2.

In one or more the embodiments under discussion, the angle (3 betweenthe line normal to a micromirror MR in the ON state and the line normalto the digital micromirror device DP is 17°, and the angle γ between thenormal to a micromirror MR in the OFF state and the normal to thedigital micromirror device DP is 17°. Accordingly, the angle between theoptical axis AX1 of the light (illumination light L1) striking thedigital micromirror device DP and the line normal to the digitalmicromirror device DP is 34°.

As described above, on the image display surface DS of the digitalmicromirror device DP, a two-dimensional image is formed throughintensity modulation on the illumination light L1. As mentioned above,the digital micromirror device DP expresses ON and OFF by driving themicromirrors MR with respect to two mutually perpendicular axes.

With reference back to FIGS. 2 to 6, the internal total reflection prismP1, the color-separating/integrating prism unit P2, the projection-sideprism P3, and the OFF-light separating prisms P4 will be described. Theinternal total reflection prism P1 has an entrance face 11, anillumination light reflecting face 12, and an exit face 13 (see FIG. 3).The entrance face 11 is inclined in such a direction that, the closer tothe screen SC, the closer to the projection optical system LN, and iswhere the illumination light L1 emitted from the illumination opticalsystem 2 enters.

The illumination light reflecting face 12 is a total reflection planeformed on the internal total reflection prism P1, and is inclined insuch a direction that, the farther away from the entrance face 11, thecloser to the color-separating/integrating prism unit P2. Theillumination light reflecting face 12 totally reflects the illuminationlight L1 entering via the entrance face 11 toward thecolor-separating/integrating prism unit P2.

The exit face 13 is disposed to face the color-separating/integratingprism unit P2, and is inclined in such a direction that, the closer tothe entrance face 11, the farther away from the projection opticalsystem LN. The exit face 13 is where the illumination light L1 totallyreflected from the illumination light reflecting face 12 exits for thecolor-separating/integrating prism unit P2.

The color-separating/integrating prism unit P2, which includes theprisms P21, P22, and P23, is what is called a Philips-type dichroicprism unit, and has the prisms P21, P23, and P22 disposed in this orderfrom the internal total reflection prism P1 toward the digitalmicromirror device DP2.

The prisms P21, P22, and P23 have entrance/exit faces 21 a, 22 a, and 23a respectively. The entrance/exit faces 21 a, 22 a, and 23 a are locatedclose to, so as to face, the OFF-light separating prisms P4respectively. The entrance/exit faces 21 a, 22 a, and 23 a are inclinedin such directions that, the closer to an OFF-light exit face 43, whichwill be described later, the farther away from the digital micromirrordevices DP1, DP2, and DP3, respectively.

An entrance/exit face 21 b (first face) disposed on the exit side of theprism P21, which is located at the most exit-side (most projectionoptical system LN-side) position in the color-separating/integratingprism unit P2, is inclined in such a direction that, the closer to theentrance face 11 of the internal total-reflection prism P1, the fartheraway from the projection optical system LN. In one or more theembodiments under discussion, the entrance/exit face 21 b is inclined atabout 11° relative to the XY plane.

The optical axis AX1 of the illumination light L1 striking, as incidentlight L11, the illumination light reflecting face 12 and the opticalaxis AX2 of the ON-light L2 (projection light) on the entrance/exit face21 b are disposed on the same plane, which is an optical axis plane AP(see FIG. 9). The optical axis plane AP is the same plane as the planeof FIG. 6. A first component vector CV1 that is obtained, when a first,outward, normal vector VN1 (see FIG. 2) to the entrance/exit face 21 bis projected onto the optical axis plane AP, by it being projected to bedisposed on the same side as the optical axis AX1 of the incident lightL11 with respect to the optical axis AX2 of the ON-light L2 points in asuch direction that, the farther away from the entrance/exit face 21 b,the farther away from the optical axis AX2 of the ON-light L2 leavingthe entrance/exit face 21 b.

The prisms P21 and P23 have, inside them, total reflection faces 21 tand 23 t respectively, and have, inside them, dichroic coat faces DR andDB respectively. The total reflection face 21 t is the inner surface ofthe entrance/exit face 21 b. The dichroic coat face DR is disposed toface the total reflection face 21 t. The total reflection face 23 t isdisposed close to, so as to face, the dichroic coat face DR. Thedichroic coat face DB is disposed close to, so as to face, the prismP22.

As shown in FIG. 4, the dichroic coat face DR and the total reflectionface 23 t are, as seen from the Y direction, inclined in such adirection that, the farther away from the digital micromirror deviceDP1, the closer to the projection optical system LN. The dichroic coatface DB is, as seen from the Y direction, inclined in such a directionthat, the farther away from the digital micromirror device DP3, thecloser to the projection optical system LN. The entrance/exit face 21 band the total reflection face 21 t are, as seen from the Y direction,perpendicular to the line normal to the digital micromirror device DP2.That is, the entrance/exit face 21 b and the total reflection face 21 tare, as seen from the Y direction, perpendicular to the optical axis AX2of the ON-light L2 reflected from the digital micromirror device DP2.

A second component vector CV2 (see FIG. 6) that is obtained, when asecond, inward, normal vector NV2 (see FIG. 4) to the dichroic coat face(opposite face) DR facing the entrance/exit face 21 b is projected ontothe optical axis plane AP, by it being projected to be disposed on thesame side as the optical axis AX1 of the incident light L11 with respectto the optical axis AX2 of the ON-light L2 points in such a directionthat, the farther away from the dichroic coat surface DR, the fartheraway from the optical axis AX2 of the ON-light L2 leaving theentrance/exit face 21 b.

A third component vector CV3 (see FIG. 6) that is obtained, when athird, inward, normal vector NV3 (see FIG. 4) to the dichroic coat faceDB is projected onto the optical axis plane AP, by it being projected tobe disposed on the same side as the optical axis AX1 of the incidentlight L11 with respect to the optical axis AX2 of the ON-light L2 pointsin such a direction that, the farther away from the dichroic coatsurface DB, the farther away from the optical axis AX2 of the ON-lightL2 leaving the entrance/exit face 21 b.

The dichroic coat face DR reflects the red component of the illuminationlight L1, and transmits the green and blue components of theillumination light L1. The dichroic coat face DB reflects the bluecomponent of the illumination light L1, and transmits the greencomponent of the illumination light L1. That is, the dichroic coat facesDR and DB reflect components of the illumination light L1 withpredetermined wavelengths and transmit components of the illuminationlight L1 with other than predetermined wavelengths. Thus, thecolor-separating/integrating prism unit P2 performs color separation onthe illumination light L1 exiting from the internal total reflectionprism P1, and then directs the resulting light toward the digitalmicromirror devices DP respectively.

The dichroic coat face DR reflects red ON-light L2, and transmits greenand blue ON-light L2. The dichroic coat face DB reflects blue ON-lightL2, and transmits green ON-light L2. That is, the dichroic coat faces DRand DB reflect ON-light L2 with predetermined wavelengths, and transmitON-light L2 with other than predetermined wavelengths. Thus, thecolor-separating/integrating prism unit P2 performs color integration onthe red, green, and blue ON-light L2 leaving the digital micromirrordevices DP1, DP2, and DP3 respectively, and then directs the resultinglight via the entrance/exit face 21 b toward the emergence side.

The prisms P21 and P23 may be disposed the other way around. That is,the prism P23 may be disposed on the emergence side of the prism P21.The color-separating/integrating prism unit P2 may be formed using,instead of what is called a Philips-type dichroic prism unit, a crossdichroic prism unit.

The projection-side prism P3 (emergence-side optical member or optic) isdisposed on the exit side (emergence side) of the prism P21 in thecolor-separating/integrating prism unit P2, and on the side oppositefrom (in FIG. 2, over) the entrance face 11 of the internal totalreflection prism P1, and has an entrance face 31 and an exit face 32(second face, emergence face). “Emergence face” refers to the face viawhich ON-light L2 is shone out of the optical unit PU toward theprojection optical system LN. The entrance face 31 is, as seen from theX direction, inclined in such a direction that, the farther away fromthe internal total-reflection prism P1, the closer to the projectionoptical system LN. The entrance face 31 is where the ON-light L2(projection light after color integration) leaving the entrance/exitface 21 b enters.

The exit face 32 is disposed to face the projection optical system LN,and is where the ON-light L2 exits such that the optical axis AX2 of theON-light L2 coincides with the direction normal to the exit face 32. Theprojection-side prism P3 serves to reduce distortion in the imageprojected on the screen SC. A projection optical system LN-side end partof the internal total reflection prism P1 protrudes from the exit face32 of the projection-side prism P3 in the emergence direction (Zdirection).

The OFF-light separating prisms P4 are disposed close to, so as to face,the entrance/exit faces 21 a, 22 a, and 23 a respectively. The OFF-lightseparating prisms P4 each have an entrance/exit face 41, an OFF-lightreflecting face 42, and an OFF-light exit face 43. The entrance/exitfaces 41 are disposed close to, so as to face, the digital micromirrordevices DP1, DP2, and DP3 respectively, and, near the digitalmicromirror devices DP1, DP2, and DP3, the optical axis AX2 of theON-light L2 coincides with the direction normal to the entrance/exitfaces 41 respectively.

The OFF-light exit faces 43 are end faces (Y-direction end faces; inFIG. 2, upper faces) opposite from the entrance face 11 of the internaltotal reflection prism P1 with respect to the optical axis AX2 of theON-light L2. The OFF-light reflecting faces 42, which are disposed nearthe digital micromirror devices DP1, DP2, and DP3 respectively, areinclined in such a way that, the closer to the OFF-light exit face 43,the farther away from the digital micromirror devices DP1, DP2, and DP3respectively. The OFF-light reflecting faces 42 totally reflect theOFF-light L3 reflected from micromirrors MR in the OFF state, andtransmit the ON-light L2 reflected from micromirrors MR in the ON state.The OFF-light exit faces 43 are where the OFF-light L3 totally reflectedfrom the OFF-light reflecting faces 42 exits from the optical unit PU.

Light absorbing members PM are provided at a distance from, so as toface, the OFF-light exit faces 43 respectively. The light absorbingmembers PM are formed as, for example, metal plates treated byblackening, and absorb the OFF-light L3 leaving the OFF-light exit faces43. This helps prevent thermal deformation of, for example, othermembers inside the projector PJ due to the OFF-light L3 exiting from theoptical unit PU.

Between the internal total reflection prism P1 and thecolor-separating/integrating prism unit P2, between thecolor-separating/integrating prism unit P2 and the projection-side prismP3, and between the color-separating/integrating prism unit P2 and theOFF-light separating prisms P4 respectively, layers of air (air gaps,unillustrated) are provided. In the color-separating/integrating prismunit P2, also between the prisms P21 and P23 and between the prisms P23and P22 respectively, layers of air are provided.

In the projector PJ configured as described above, white light emittedfrom the light source 1 (see FIG. 1) is converged by the illuminationoptical system 2 (see FIG. 1) so that white illumination light L1 isemitted toward the optical unit PU.

The white illumination light L1 enters the internal total-reflectionprism P1 via the entrance face 11, and is then totally reflected on theillumination light reflecting face 12. The white illumination light L1totally reflected from the illumination light reflecting face 12 exitsvia the exit face 13, and then enters the prism P21 in thecolor-separating/integrating prism unit P2 via the entrance/exit face 21b.

The white illumination light L1 having entered the prism P21 in thecolor-separating/integrating prism unit P2 then strikes the dichroiccoat face DR, where the red component of the illumination light L1 isreflected, and the green and blue components are transmitted. The greenand blue components of the illumination light L1 transmitted through thedichroic coat face DR enters the prism P23, where the blue component isreflected on the dichroic coat face DB while the green component istransmitted through the dichroic coat face DB to enter the prism P22.

The red component of the illumination light L1 reflected from thedichroic coat face DR, the blue component of the illumination light L1reflected from the dichroic coat face DB, and the green component of theillumination light L1 transmitted through the dichroic coat faces DR andDB exits via the entrance/exit faces 21 a, 23 a, and 22 a respectively,and then enter the OFF-light separating prisms P4 respectively. The red,green, and blue components of the illumination light L1 transmittedthrough the OFF-light separating prisms P4 respectively exit via theentrance/exit faces 41, then passes through the cover glasses CG tostrike the digital micromirror devices DP1, DP3, and DP2 respectively.Thus, the color-separating/integrating prism unit P2 performs colorseparation on the illumination light L1 totally reflected from theillumination light reflecting face 12, and directs the resulting lighttoward the digital micromirror devices DP1, DP2, and DP3 respectively.

The red, green, and blue ON-light L2 reflected from micromirrors MR inthe ON state in the digital micromirror devices DP1 to and DP3 entersthe OFF-light separating prisms P4 via the entrance/exit faces 41respectively, and then passes through the OFF-light reflecting faces 42to enter, through the entrance/exit faces 21 a, 22 a, and 23 arespectively, the prisms P21, P22, and P23 in thecolor-separating/integrating prism unit P2.

Red ON-light L2, having been totally reflected on the total reflectionface 21 t of the prism P21, is then reflected on the dichroic coat faceDR to be directed to the entrance/exit face 21 b. Green ON-light L2,having been transmitted through the prism P22, then passes through thedichroic coat faces DB and DR in this order to be directed to theentrance/exit face 21 b. Blue ON-light L2, having been totally reflectedon the total reflection face 23 t of the prism P23, is reflected on thedichroic coat face DB, and is then transmitted through the dichroic coatface DR to be directed to the entrance/exit face 21 b. Meanwhile, red,green, and blue ON-light L2, as it passes through thecolor-separating/integrating prism unit P2, undergoes color integration,and the color-integrated ON-light L2 exits via the entrance/exit face 21b toward the emergence side.

The ON-light L2 (projection light after color integration) having exitedvia the entrance/exit face 21 b enters the projection-side prism P3 viathe entrance face 31. The ON-light L2 having entered the projection-sideprism P3 is transmitted through it to exit via the exit face 32 towardthe projection optical system LN.

Here, as shown in FIG. 6, the illumination light reflecting face 12 isdisposed outside the beam of the ON-light L2. That is, the ON-light L2does not strike the illumination light reflecting face 12. Thus, thebeam of the illumination light L1 and the beam of the ON-light L2 can beseparated from each other within the Z-direction distance D1 (in one ormore the embodiments under discussion, about 85 mm) between theentrance/exit face 41 of the OFF-light separating prism P4 correspondingto the digital micromirror device DP2 and the exit face 32.

A color-separating/integrating prism unit P2-side end part of the beamof the illumination light L1 on the illumination light reflecting face12 is disposed on the same side as the color-separating/integratingprism unit P2 with respect to the exit face 32. That is, acolor-separating/integrating prism unit P2-side end part LE (see FIG. 6)of the region resulting from the beam of the illumination light L1 onthe illumination light reflecting face 12 being projected onto theoptical axis plane AP is disposed on the same side as thecolor-separating/integrating prism unit P2 with respect to the exit face32. Moreover, the intersection line NL between the illumination lightreflecting face 12 and the exit face 32 is disposed outside the beam ofthe ON-light L2 on the exit face 32. Thus, the beam of the ON-light L2on the exit face 32 does not overlap with the beam of the illuminationlight L1 on the illumination light reflecting face 12. Here, the“intersection line NL between the illumination light reflecting face 12and the exit face 32” refers to the intersection line of the planeincluding and parallel to the exit face 32 with the illumination lightreflecting face 12.

The plane (in one or more the embodiments under discussion, the sameplane as the optical axis plane AP) that includes the optical axis AX2of the ON-light L2 leaving the entrance/exit face 21 b and that passesthrough the center of the digital micromirror device DP2 in itslonger-side direction and runs parallel to its shorter-side direction isperpendicular to the illumination light reflecting face 12.

The ON-light L2 that has entered the projection optical system LN isprojected onto the screen SC (see FIG. 1). Thus, the color imagedisplayed on the digital micromirror devices DP is projected onto thescreen SC. Meanwhile, the actuator 4 performs zooming and focusing. Theprojection-side prism P3 shines out the ON-light L2 via the exit face 32such that the optical axis AX2 coincides with the direction normal tothe exit face 32. In this way, it is possible to reduce distortion inthe image projected on the screen SC on an enlarged scale.

The actuator 4 permits the projection lenses 51 and 52 in the projectionoptical system LN to be moved in the Y direction, and thereby permitsthe projection position of the projected image to be changed in the Ydirection. For example, in a case where the projector PJ is installed ona ceiling surface in a room (unillustrated), the projection lenses 51and 52 are moved toward the internal total reflection prism P1 (in FIG.5, downward). The projector PJ can then project an image on the screenSC at a position away from the ceiling.

Here, the first component vector CV1 points in such a direction that,the farther away from the entrance/exit face 21 b, the farther away fromthe optical axis AX2 of the ON-light L2 leaving the entrance/exit face21 b. Thus, even when the distance D2 between the optical axis AX2 ofthe ON-light L2 on the exit face 32 and the intersection line NL isincreased, of all the rays of the illumination light L1 directed to theinternal total reflection prism P1, even thecolor-separating/integrating prism unit P2-side rays of the illuminationlight L1 enter via the entrance face 11 so as to be totally reflected onthe illumination light reflecting face 12.

On the other hand, the OFF-light L3 reflected from micromirrors MR inthe OFF state in the digital micromirror devices DP1, DP2, and DP3enters the OFF-light separating prisms P4 via the entrance/exit faces41, is then totally reflected on the OFF-light reflecting faces 42, andis then discharged out of the optical unit PU via the OFF-light exitfaces 43. The OFF-light L3 discharged out of the optical unit PU isabsorbed by the light absorbing members PM. This helps prevent theOFF-light L3 from entering the projection optical system LN. It is thuspossible to prevent a drop in the contrast of the projected image.

Here, the light absorbing members PM are provided away from theOFF-light exit faces 43. This helps reduce the heat that conducts fromthe light absorbing members PM having absorbed the OFF-light L3 to theoptical unit PU. It is thus possible to suppress a rise in thetemperature of the optical unit PU, and to prevent, for example, thermaldeformation of the optical unit PU. This helps prolong the lifetime ofthe optical unit PU and the projector PJ.

The illumination light L1 (flat light) reflected on micromirrors MR inthe middle of shifting from one to the other of the ON and OFF states isreflected in the direction opposite, with respect to the directionnormal to the micromirrors MR, to the illumination light L1 as theincident light. The flat light and the illumination light L1 reflectedfrom the cover glasses CG enter the OFF-light separating prisms P4 andthen exit via the OFF-light exit faces 43. It is thus possible toprevent the flat light or the illumination light L1 reflected from thecover glasses CG from entering the projection optical system LN. Thishelps further prevent a drop in the contrast of the projected image.

Here, in each of the OFF-light separating prisms P4, the angle θ_(ON) ofincidence of the ray of ON-light L2 with the largest angle of incidencewith respect to the OFF-light reflecting face 42 and the angle θ_(OFF)of incidence of the ray of OFF-light L3 with the smallest angle ofincidence with respect to the OFF-light reflecting face 42 fulfillconditional formula (1) below, because then the OFF-light reflectingface 42 transmits the ON-light L2 and almost totally reflects theOFF-light L3.

θ_(OFF)>sin⁻¹(1/n)>θ_(ON)  (1)

where

-   -   θ_(ON) represents the angle of incidence of the ray of ON-light        L2 with the largest angle of incidence with respect to the        OFF-light reflecting face 42;    -   θ_(OFF) represents the angle of incidence of the ray of        OFF-light L3 with the smallest angle of incidence with respect        to the OFF-light reflecting face 42; and    -   n represents the index of refraction of the OFF-light separating        prisms P4.

For example, in a case where the index of refraction of the OFF-lightseparating prisms P4 is 1.5168, setting the angle of incidence θ_(ON) at36.5° and setting the angle of incidence θ_(OFF) at 43.7° allowsconditional formula (1) to be fulfilled, and thus permits the OFF-lightreflecting face 42 to transmit the ON-light L2 while almost totallyreflecting the OFF-light L3.

Between the projector PJ employing the optical unit PU according to oneor more the embodiments under discussion and a projector employing anoptical unit according to a comparative example, the up-down shiftamount (Y-direction shift amount) of the projection optical system LNwas compared.

FIG. 10 is a side sectional view of the optical unit of the comparativeexample. For convenience' sake, such parts as find their counterparts inthe optical unit PU of one or more the embodiments under discussion areidentified by common reference signs. In the comparative example, theentrance/exit face 21 b of the prism P21 in thecolor-separating/integrating prism unit P2 is perpendicular to theoptical axis AX2 of the color-integrated ON-light L2. In the comparativeexample, the projection-side prism P3 is omitted. Accordingly, while theemergence face in one or more the embodiments under discussion coincideswith the exit face 32 of the projection-side prism P3, the emergenceface in the comparative example coincides with the entrance/exit face 21b of the prism P21. Otherwise, the comparative example is structuredsimilarly to the optical unit PU of one or more the embodiments underdiscussion. The up-down shift amount is the distance D2 (see FIGS. 6 and10) between the optical axis AX2 of the ON-light L2 on the emergenceface and the intersection line NL. The Z-direction distance D1 betweenthe entrance/exit face 41 facing the digital micromirror device DP2 andthe exit face 32 is 85 mm in both one or more the embodiments underdiscussion and the comparative example. The angle of inclination of theillumination light reflecting face 12 relative to the XZ plane is thesame in one or more the embodiments under discussion and the comparativeexample.

While the up-down shift amount of the projection optical system LN inthe projector PJ according to one or more the embodiments underdiscussion was 26.6 mm, the up-down shift amount of the projectionoptical system in the projector of the comparative example was 19.0 mmThat is, the up-down shift amount when the optical unit PU according toone or more the embodiments under discussion is used is 7.6 mm longerthan that in the comparative example. Thus, the up-down shift amount ofthe projection optical system LN in the projector PJ provided with theoptical unit PU according to one or more the embodiments underdiscussion can be made longer than that in the comparative example. Inone or more the embodiments under discussion and the comparativeexample, the f-number of the illumination light L1 was approximately thesame, and the luminance of the projected image was approximately thesame.

According to one or more the embodiments under discussion, a firstcomponent vector CV1 that is obtained, when a first, outward, normalvector NV1 to the entrance/exit face 21 b is projected onto the opticalaxis plane AP, by it being projected to be disposed on the same side asthe optical axis AX1 of the incident light L11 with respect to theoptical axis AX2 of the ON-light L2 points in such a direction that, thefarther away from the entrance/exit face 21 b, the farther away from theoptical axis AX2 of the ON-light L2 leaving the entrance/exit face 21 b.Thus, even when the distance D2 between the optical axis AX2 of theON-light L2 on the exit face 32 (emergence face) and the intersectionline NL is increased, of all the rays of the illumination light L1directed to the internal total reflection prism P1, even thecolor-separating/integrating prism unit P2-side rays of the illuminationlight L1 enter via the entrance face 11 so as to be totally reflected onthe illumination light reflecting face 12. Thus, when the projectionoptical system LN is arranged, it is possible, while preventing a dropin the amount of light in the emergent ON-light L2 (projection light),to increase the Y-direction shift amount of the projection opticalsystem LN, and thereby to enhance the usability of the optical unit PU.

The prisms P21 (first prism) and P23 (first prism) have dichroic coatfaces DR and DB respectively, and the color-separating/integrating prismunit P2 (prism unit) performs color separation on the illumination lightL1 and color integration on the ON-light L2 (projection light). It isthus possible to separate white illumination light into colors easilyand to integrate projection light of different colors easily.

A second component vector CV2 that is obtained, when a second, inward,normal vector NV2 to the dichroic coat face (opposite face) DR facingthe entrance/exit face 21 b of the prism P21 (first prism) having theentrance/exit face 21 b is projected onto the optical axis plane AP, byit being projected to be disposed on the same side as the optical axisAX1 of the incident light L11 with respect to the optical axis AX2points in such a direction that, the farther away from the dichroic coatsurface DR, the farther away from the optical axis AX2 of the ON-lightL2 leaving the entrance/exit face 21 b. It is thus possible, whileinclining the entrance/exit face 21 b, to give the prism P21 asufficient Z-direction length, and thus to further prevent a drop in theamount of light in the illumination light L1 directed to the digitalmicromirror devices DP.

The illumination light reflecting face 12 is disposed outside the beamof the ON-light L2. Thus, the beam of the illumination light L1 and thebeam of the ON-light L2 can be separated from each other with theZ-direction distance D1 between the entrance/exit face 41 facing thedigital micromirror device DP2 and the exit face 32. Accordingly, theON-light L2 does not passes through the illumination light reflectingface 12, and thus, compared with a structure where the projection-sideprism P3 is disposed close to, so as to face, the illumination lightreflecting face 12, there are less layers of air (air gaps) throughwhich the ON-light L2 passes. It is thus possible to enhance thetransmittance for the ON-light L2 through the optical unit PU, andthereby to enhance the quality of the projected image.

The illumination light reflecting face 12 is constituted by the totalreflection face in the internal total reflection prism P1 (reflectingmember). Thus, the cross section of the beam of the illumination lightL1 on the illumination light reflecting face 12 is smaller than thecross section of the beam of the illumination light L1 before strikingthe entrance face 11. It is thus possible, while suppressing an increasein the size of the illumination light reflecting face 12, to furtherprevent a drop in the amount of light in the ON-light L2. It is alsopossible to enhance the efficiency of reflection on the illuminationlight L1 reflecting face 12, and to still further prevent a drop in theamount of light in the ON-light L2.

The projection-side prism P3 (emergence-side optical member) is providedwhich has an exit face 32 (second face) in the direction of the normalto which the optical axis AX2 of the ON-light L2 (projection light) isdisposed and via which the ON-light L2 exits, and the projection-sideprism P3 is disposed on the ON-light L2's exits direction side of theentrance/exit face 21 b. It is thus possible to reduce distortion in theprojected image. A color-separating/integrating prism unit P2 (prismunit)-side end part of the beam of the illumination light L1 on theillumination light reflecting face 12 is disposed on the same side ofthe color-separating/integrating prism unit P2 with respect to the exitface 32, and the intersection line NL between the illumination lightreflecting face 12 and the exit face 32 is disposed outside the beam ofthe ON-light L2 on the exit face 32. It is thus possible to morereliably obtain a satisfactory Y-direction shift amount of theprojection optical system LN.

A plurality of fitting portions for the fitting of the digitalmicromirror devices DP are provided, and these fitting portions aredisposed to correspond to the prisms P21 to P23 respectively. Thedigital micromirror device DP forms an image through intensitymodulation on the illumination light L1 resulting from ON/OFF control ofthe inclination of each of a plurality of micromirrors MR that pivotabout a pivot axis. Thus, it is possible to easily fit the digitalmicromirror devices DP to the optical unit PU, and thereby to easilyobtain an optical unit PU that can emit projection light generated bythe digital micromirror devices DP.

Each micromirror MR has two mutually perpendicular pivot axes, and thedriving of each micromirror MR is performed about the two pivot axes.This helps enhance the luminance of the projected image. The plane thatincludes the optical axis AX2 of the ON-light L2 leaving theentrance/exit face 21 b and that passes through the center of thedigital micromirror device DP2 (one of the digital micromirror devicesDP) in its longer-side direction and runs parallel to its shorter-sidedirection is perpendicular to the illumination light reflecting face 12.This helps make the cross section of the beam of the illumination lightL1 smaller, and it is thus possible to more reliably direct the beam ofthe illumination light L1 to the illumination light reflecting face 12.

Between the digital micromirror devices DP1, DP2, and DP3 and the prismsP21, P22, and P23 respectively, the OFF-light separating prisms P4(third prisms) are disposed. The OFF-light separating prisms P4 haveOFF-light reflecting faces 42 that transmit the ON-light L2 (projectionlight) reflected from micromirrors MR in the ON state in the digitalmicromirror devices DP and that reflect the OFF-light L3 (unnecessarylight) reflected from micromirrors MR in the OFF state in the digitalmicromirror devices DP. Thus, the OFF-light L3 can be discharged out ofthe optical unit PU without being directed to thecolor-separating/integrating prism unit P2. Thus, it is possible toprevent the OFF-light L3 from entering the projection lenses 51 and 52in the projection optical system LN. It is thus possible to preventgeneration of stray light, and to enhance the contrast of the projectedimage.

Fulfilling conditional formula (1) permits the OFF-light reflectingfaces 42 to transmit the ON-light L2 and almost totally reflect theOFF-light L3.

The projector PJ includes the optical unit PU, the light source 1, theillumination optical system 2 which emits illumination light L1 towardthe internal total reflection prism P1 (reflecting member), and theprojection optical system LN which projects the image displayed on thedigital micromirror devices DP fitted to the fitting portions onto thescreen SC on an enlarged scale. It is thus possible to easily build aprojector PJ provided with the optical unit PU.

The projection optical system LN is disposed to face the entrance/exitface 21 b of the optical unit PU, and the internal total reflectionprism P1 is disposed below the optical axis AX2 of the ON-light L2leaving the entrance/exit face 21 b. The projection optical system LNcan move up and down. It is thus possible to easily build a projector PJthat allows up and downward shifting.

Next, one or more embodiments of the present invention will bedescribed. FIGS. 11 to 14 are a perspective view, a top view, a sideview, and a side sectional view, respectively, of an optical unit PUaccording to one or more embodiments. For convenience's sake, such partsas find their counterparts in one or more embodiments shown in FIGS. 1to 9 are identified by common reference numerals. In one or moreembodiments, the entrance/exit face 21 b (first face) of thecolor-separating/integrating prism unit P2 is structured differentlythan in one or more embodiments described above; otherwise, thestructure here is similar to that in one or more embodiments describedabove.

The entrance/exit face 21 b of the prism P21 in thecolor-separating/integrating prism unit P2 according to one or moreembodiments is, as seen from the Y direction, inclined in such adirection that, the farther away from the digital micromirror deviceDP1, the farther away from the projection optical system LN. Theprojection-side prism P3 is, as seen from the Y direction, in atriangular shape.

The operation of the projector PJ provided with the optical unit PUstructured as described is similar to that in one or more embodimentsdescribed above.

Between the projector PJ employing the optical unit PU according to oneor more embodiments and a projector employing an optical unit accordingto a comparative example, the up-down shift amount (Y-direction shiftamount) of the projection optical system LN was compared. In thecomparative example, as in FIG. 10, the first component vector CV1 isparallel to the optical axis AX2 of the ON-light L2 leaving theentrance/exit face 21 b. In both one or more embodiments and thecomparative example, the emergence face coincides with the exit face 32of the projection-side prism P3. Otherwise, the comparative example wasstructured similarly to the optical unit PU according to one or moreembodiments. The up-down shift amount was measured in a similar manneras in one or more embodiments described above. The Z-direction distanceD1 between the entrance/exit face 41 facing the digital micromirrordevice DP2 and the exit face 32 is 85 mm in both one or more embodimentsand the comparative example. The angle of inclination of theillumination light reflecting face 12 relative to the XZ plane is thesame in one or more embodiments and the comparative example.

While the up-down shift amount of the projection optical system LN inthe projector PJ employing the optical unit PU according to one or moreembodiments was 31.5 mm, the up-down shift amount of the projectionoptical system in the projector employing the optical unit of thecomparative example was 27.6 mm That is, the up-down shift amount whenthe optical unit PU according to one or more embodiments is used is 3.9mm longer than that in the comparative example. Thus, the up-down shiftamount of the projection optical system LN in the projector PJ providedwith the optical unit PU according to one or more embodiments can bemade longer than that in the comparative example. In one or moreembodiments and the comparative example, the f-number of theillumination light L1 was approximately the same, and the luminance ofthe projected image was approximately the same.

Also with one or more embodiments, it is possible to obtain similareffects as with one or more embodiments described above.

Next, one or more embodiments of the present invention will bedescribed. FIGS. 15 to 18 are a perspective view, a top view, a sideview, and a side sectional view, respectively, of an optical unit PUaccording to one or more embodiments. For convenience's sake, such partsas find their counterparts in one or more embodiments shown in FIGS. 1to 9 are identified by common reference numerals. In one or moreembodiments, the color-separating/integrating prism unit P2 isstructured differently than in one or more embodiment described above;otherwise, the structure here is similar to that in one or moreembodiments described above.

In one or more embodiments, the color-separating/integrating prism unitP2 is composed of prisms P21 and P22, and thus compared with thecolor-separating/integrating prism unit P2 in one or more embodimentsdescribed above, the prism P23 is omitted. Also the digital micromirrordevice DP3 corresponding to the prism P23 is omitted. The light source 1comprises a UHP lamp, and between the light source 1 and theillumination optical system 2, a color wheel (unillustrated) isdisposed.

The operation of the projector PJ provided with the optical unit PUstructured as described above is, after the illumination light L1 entersvia the entrance face 11, similar to that in one or more embodimentsdescribed above. In one or more embodiments, the red component of theillumination light L1 strikes the digital micromirror device DP1, andthe green and blue components of the illumination light L1 having passedthrough the color wheel alternately strike the digital micromirrordevice DP2.

Between the projector PJ employing the optical unit PU according to oneor more embodiments and a projector employing an optical unit accordingto a comparative example, the up-down shift amount (Y-direction shiftamount) of the projection optical system LN was compared. In thecomparative example, as in the structure shown in FIG. 10, theentrance/exit face 21 b of the prism P21 in thecolor-separating/integrating prism unit P2 is perpendicular to theoptical axis AX2 of the color-integrated ON-light L2. In the comparativeexample, the projection-side prism P3 is omitted. Thus, the emergenceface in one or more embodiments coincides with the exit face 32 of theprojection-side prism P3, and the emergence face in the comparativeexample coincides with the entrance/exit face 21 b of the prism P21.Otherwise, the comparative example was structured similarly to theoptical unit PU according to one or more embodiments. The up-down shiftamount was measured in a similar manner as in one or more embodimentsdescribed above. The Z-direction distance D1 between the entrance/exitface 41 facing the digital micromirror device DP2 and the exit face 32is 85 mm in both one or more embodiments and the comparative example.The angle of inclination of the illumination light reflecting face 12relative to the XZ plane is the same in one or more embodiments and thecomparative example.

While the up-down shift amount of the projection optical system LN inthe projector PJ employing the optical unit PU according to one or moreembodiments was 30.5 mm, the up-down shift amount of the projectionoptical system in the projector employing the optical unit of thecomparative example was 19.0 mm That is, the up-down shift amount whenthe optical unit PU according to one or more embodiments is used is 11.5mm longer than that in the comparative example. Thus, the up-down shiftamount of the projection optical system LN in the projector PJ providedwith the optical unit PU according to one or more embodiments can bemade longer than that in the comparative example. In one or moreembodiments and the comparative example, the f-number of theillumination light L1 was approximately the same, and the luminance ofthe projected image was approximately the same.

Also with one or more embodiments, it is possible to obtain similareffects as with one or more embodiments described above. Moreover, it ispossible to reduce, as compared with one or more embodiments describedabove, the number of digital micromirror devices DP, which areexpensive.

Next, one or more embodiments of the present invention will bedescribed. FIGS. 19 to 21 are a perspective view, a side view, and aside sectional view, respectively, of an optical unit PU according toone or more embodiments. For convenience's sake, such parts as findtheir counterparts in one or more embodiments shown in FIGS. 1 to 9 areidentified by common reference numerals. In one or more embodiments, theillumination light reflecting face 12 is structured differently than inone or more embodiments described above; otherwise, the structure hereis similar to that in one or more embodiments described above.

The optical unit PU according to one or more embodiments includes,instead of an internal total reflection prism P1, a mirror member 80(mirror or reflecting member) having a mirror face 80 a formed on aglass substrate 81. The illumination light reflecting face 12 isconstituted by the mirror face 80 a. The mirror face 80 a is formed bycoating a high-precision polished glass substrate 81 with a metal (forexample, aluminum or silver) or a dielectric multilayer film on a vacuumdeposition machine.

In the projector PJ provided with the optical unit PU structured asdescribed above, the white illumination light L1 emitted from theillumination optical system 2 strikes the mirror face 80 a of the mirrormember 80. The illumination light L1 striking the mirror face 80 a isreflected on the mirror face 80 a, and then enters thecolor-separating/integrating prism unit P2 via the entrance/exit face 21b. The operation thereafter of the projector PJ of one or moreembodiments is similar to that in one or more embodiments describedabove.

Between the projector PJ employing the optical unit PU according to oneor more embodiments and a projector employing an optical unit accordingto a comparative example, the up-down shift amount (Y-direction shiftamount) of the projection optical system LN was compared. In thecomparative example, as in the structure shown in FIG. 10, theentrance/exit face 21 b of the prism P21 in thecolor-separating/integrating prism unit P2 is perpendicular to theoptical axis AX2 of the color-integrated ON-light L2. In the comparativeexample, the projection-side prism P3 is omitted. Thus, the emergenceface in one or more embodiments coincides with the exit face 32 of theprojection-side prism P3, and the emergence face in the comparativeexample coincides with the entrance/exit face 21 b of the prism P21.Otherwise, the comparative example was structured similarly to theoptical unit PU according to one or more embodiments. The up-down shiftamount was measured in a similar manner as in one or more embodimentsdescribed above. The Z-direction distance D1 between the entrance/exitface 41 facing the digital micromirror device DP2 and the exit face 32is 85 mm in both one or more embodiments and the comparative example.The angle of inclination of the illumination light reflecting face 12relative to the XZ plane is the same in one or more embodiments and thecomparative example.

While the up-down shift amount of the projection optical system LN inthe projector PJ employing the optical unit PU according to one or moreembodiments was 30.4 mm, the up-down shift amount of the projectionoptical system in the projector employing the optical unit of thecomparative example was 18.0 mm That is, the up-down shift amount whenthe optical unit PU according to one or more embodiments is used is 12.4mm longer than that in the comparative example. Thus, the up-down shiftamount of the projection optical system LN in the projector PJ providedwith the optical unit PU according to one or more embodiments can bemade longer than that in the comparative example. In one or moreembodiments and the comparative example, the f-number of theillumination light L1 was approximately the same, and the luminance ofthe projected image was approximately the same.

Even when the illumination light reflecting face 12 is constituted bythe mirror face 80 a of the mirror member 80 as in one or moreembodiments, it is possible to obtain similar effects as with one ormore embodiments described above.

Next, one or more embodiments of the present invention will bedescribed. FIGS. 22 to 25 are a perspective view, a top view, a sideview, and a side sectional view, respectively, of an optical unit PUaccording to one or more embodiments. For convenience's sake, such partsas find their counterparts in one or more embodiments shown in FIGS. 1to 9 are identified by common reference numerals. In one or moreembodiments, the digital micromirror devices DP are structureddifferently than in tone or more embodiments described above; otherwise,the structure here is similar to that in one or more embodimentsdescribed above.

In one or more embodiments, the entrance face 31 of the projection-sideprism P3 is composed of a face 31 a that is located close to, so as toface, the entrance/exit face 21 b and a face 31 b that is located closeto, so as to face, the illumination light reflecting face 12. The faces31 a and 31 b abut each other in the Y direction. An internal totalreflection prism P1-side end part of the exit face 21 is close to theillumination light reflecting face 12.

FIG. 26 is a perspective view of micromirrors MR in ON and OFF states ina digital micromirror device DP in one or more embodiments. The digitalmicromirror devices DP in one or more embodiments differs, in that themicromirrors MR pivot about one pivot axis RA, from the digitalmicromirror devices DP in one or more embodiments described above, wherethe micromirrors MR pivot about two mutually perpendicular axes.Otherwise, the digital micromirror devices DP in one or more embodimentsare similar to those in one or more embodiments described above.

The angles β and γ are each 12°. Thus, a micromirror MR pivots about thepivot axis RA from the reference state (the state where the directionnormal to the micromirror MR coincides with the Z direction) through−12° to turn to the ON state or through +12° to turn to the OFF state.Thus, the digital micromirror devices DP express ON and OFF by drivingthe micromirrors MR with respect to one pivot axis RA. Near the digitalmicromirror devices DP, the optical axis AX1 of the illumination lightL1, the optical axis AX2 of the ON-light L2, and the optical axis AX3 ofthe OFF-light L3 are disposed on the same plane.

In the projector PJ provided with the optical unit PU structured asdescribed above, when white illumination light L1 is emitted from theillumination optical system 2, as in one or more embodiments describedabove, ON-light L2 (projection light) is emitted from the optical unitPU. Thus, a projected image is projected onto the screen SC.

At that time, part of the ON-light L2 leaving the entrance/exit face 21b of the prism P21 enters the internal total reflection prism P1 via theexit face 13, then passes through the illumination light reflecting face12, and then enters the projection-side prism P3. Thereafter, theON-light L2 exits via the exit face 32 of the projection-side prism P3.

In one or more embodiments and those described above, the angle θ(unillustrated) between the optical axis AX1 of the light striking thedigital micromirror devices DP and the optical axis AX2 of the ON-lightL2 (reflected light) reflected from micromirrors MR in the ON state is34° and 24° respectively. That is, the angle θ in one or moreembodiments is smaller than the angle θ in one or more embodimentsdescribed above. Accordingly, within the same distance D1 as in one ormore embodiments described above, the ON-light L2 and the illuminationlight L1 cannot be separated from each other completely; thus, unlike inone or more embodiments described above, the ON-light L2 passes throughthe illumination light reflecting face 12.

On the other hand, the OFF-light L3 (unnecessary light) reflected frommicromirrors MR in the OFF state in the digital micromirror devices DP1,DP2, and DP3 is discharged out of the optical unit PU via the top faces(end faces opposite from the entrance face 11 in the Y direction) andupper parts of the entrance/exit faces 21 b of the prisms P21, P22, andP23.

Between the projector PJ employing the optical unit PU according to oneor more embodiments and a projector employing an optical unit accordingto a comparative example, the up-down shift amount (Y-direction shiftamount) of the projection optical system LN was compared. In thecomparative example, as in the structure shown in FIG. 10, theentrance/exit face 21 b of the prism P21 in thecolor-separating/integrating prism unit P2 is perpendicular to theoptical axis AX2 of the color-integrated ON-light L2. In both one ormore embodiments and the comparative example, the emergence facecoincides with the exit face 32 of the projection-side prism P3.Otherwise, the comparative example was structured similarly to theoptical unit PU according to one or more embodiments. The up-down shiftamount was measured in a similar manner as in one or more embodiments.The Z-direction distance D1 between the entrance/exit face 41 facing thedigital micromirror device DP2 and the exit face 32 is 86 mm in both oneor more embodiments and the comparative example. The angle ofinclination of the illumination light reflecting face 12 relative to theXZ plane is the same in one or more embodiments and the comparativeexample.

While the up-down shift amount of the projection optical system LN inthe projector PJ according to one or more embodiments was 38.2 mm, theup-down shift amount of the projection optical system in the projectoremploying the optical unit of the comparative example was 25.1 mm Thatis, the up-down shift amount when the optical unit PU according to oneor more embodiments is used is 13.1 mm longer than that in thecomparative example. Thus, the up-down shift amount of the projectionoptical system LN in the projector PJ provided with the optical unit PUaccording to one or more embodiments can be made longer than that in thecomparative example. In one or more embodiments and the comparativeexample, the f-number of the illumination light L1 was approximately thesame, and the luminance of the projected image was approximately thesame.

Also with one or more embodiments, it is possible to obtain similareffects as with one or more embodiments described above.

Next, one or more embodiments of the present invention will bedescribed. FIGS. 27 to 29 are a perspective view, a top view, and a sidesectional view, respectively, of an optical unit PU according to one ormore embodiments. For convenience's sake, such parts as find theircounterparts in one or more embodiments shown in FIGS. 22 to 26 areidentified by common reference numerals. In one or more embodiments, thecolor-separating/integrating prism unit P2 is structured differentlythan in one or more embodiments described above; otherwise, thestructure here is similar to that in one or more embodiments describedabove.

In one or more embodiments, the color-separating/integrating prism unitP2 is composed of prisms P21 and P22, and thus compared with thecolor-separating/integrating prism unit P2 in one or more embodimentsdescribed above, the prism P23 is omitted. As in one or more embodimentsdescribed above, the color-separated illumination light L1 is directedto the digital micromirror devices DP1 and DP2, and the color-integratedON-light L2 exits via the exit face 32. Also in one or more embodiments,as in one or more embodiments described above, the ON-light L2 passesthrough the illumination light reflecting face 12.

Between the projector PJ employing the optical unit PU according to oneor more embodiments and a projector employing an optical unit accordingto a comparative example, the up-down shift amount (Y-direction shiftamount) of the projection optical system LN was compared. In thecomparative example, as in the structure shown in FIG. 10, theentrance/exit face 21 b of the prism P21 in thecolor-separating/integrating prism unit P2 is perpendicular to theoptical axis AX2 of the color-integrated ON-light L2. In both one ormore embodiments and the comparative example, the emergence facecoincides with the exit face 32 of the projection-side prism P3.Otherwise, the comparative example was structured similarly to theoptical unit PU according to one or more embodiments. The up-down shiftamount was measured in a similar manner as in one or more embodimentsdescribed above. The Z-direction distance D1 between the entrance/exitface 41 facing the digital micromirror device DP2 and the exit face 32is 86 mm in both one or more embodiments and the comparative example.The angle of inclination of the illumination light reflecting face 12relative to the XZ plane is the same in one or more embodiments and thecomparative example.

While the up-down shift amount of the projection optical system LN inthe projector PJ employing the optical unit PU according to one or moreembodiments was 38.2 mm, the up-down shift amount of the projectionoptical system in the projector employing the optical unit of thecomparative example was 25.1 mm That is, the up-down shift amount whenthe optical unit PU according to one or more embodiments is used is 13.1mm longer than that in the comparative example. Thus, the up-down shiftamount of the projection optical system LN in the projector PJ providedwith the optical unit PU according to one or more embodiments can bemade longer than that in the comparative example. In one or moreembodiments and the comparative example, the f-number of theillumination light L1 was approximately the same, and the luminance ofthe projected image was approximately the same.

Also with one or more embodiments, it is possible to obtain similareffects as with one or more embodiments described above.

One or more embodiments of the present invention find application inoptical units that receive illumination light and emit projection lightreflected from a digital micromirror device, and in projectors providedwith such optical units. As will be understood from the abovedescription, one or more embodiments described above encompass, amongothers, the following distinctive structures (#1) to (#14).

(#1) An optical unit in which illumination light is directed to aplurality of digital micromirror devices that produce projection lightby modulating the illumination light on an image display surfaceaccording to an image signal so that the optical unit emits, bytransmitting, the projection light produced by the plurality of digitalmicromirror devices includes: a reflecting member having an illuminationlight reflecting face on which the illumination light is reflected; anda prism unit composed of a plurality of first prisms, the illuminationlight reflected from the illumination light reflecting face entering viaa first face of the most emergence-side first prism, the projectionlight exiting via the first face. The reflecting member is close to thefirst face and is disposed so as to protrude from the first face in theprojection light exiting direction. The optical axis of the illuminationlight striking, as incident light, the illumination light reflectingface and the optical axis of the projection light on the first face aredisposed on the same plane which is the optical axis plane. A firstcomponent vector that is obtained, when a first, outward, normal vectorto the first face is projected onto the optical axis plane, by it beingprojected to be disposed on the same side as the optical axis of theincident light with respect to the optical axis of the projection lightpoints in such a direction that, the farther away from the first face,the farther away from the optical axis of the projection light leavingthe first face.

(#2) In the optical unit according to (#1), at least one of the firstprisms has a dichroic coat face, and the prism unit performs colorseparation for the illumination light and color integration for theprojection light.

(#3) In the optical unit according to (#1) or (#2), a second componentvector that is obtained, when a second, inward, normal vector to anopposite face facing the first face of the first prism having the firstface is projected onto the optical axis plane, by it being projected tobe disposed on the same side as the optical axis of the incident lightwith respect to the optical axis of the projection light points in sucha direction that, the farther away from the opposite face, the fartheraway from the optical axis of the projection light leaving the firstface.

(#4) In the optical unit according to any one of (#1) to (#3), theillumination light reflecting face is disposed outside the beam of theprojection light.

(#5) In the optical unit according to any one of (#1) to (#4), thereflecting member is an internal total reflection prism, and theillumination light reflecting face is constituted by a total reflectionface in the internal total reflection prism.

(#6) In the optical unit according to any one of (#1) to (#4), thereflecting member is a mirror member, and the illumination lightreflecting face is constituted by a mirror face in the mirror member.

(#7) In the optical unit according to any one of (#1) to (#6), there isfurther provided an emergence-side optical member having a second face,the optical axis of the projection light being disposed in a directionnormal to the second face, the projection light emerging from the secondface, the emergence-side optical member being disposed on the projectionlight exiting direction side of the first face. A prism unit-side endpart of the beam of the illumination light on the illumination lightreflecting face is disposed on the same side as the prism unit withrespect to the second face, and the intersection line between theillumination light reflecting face and the second face is disposedoutside the beam of the projection light on the second face.

(#8) In the optical unit according to (#7), the emergence-side opticalmember is a second prism, the projection light entering via an entranceface thereof facing the first face, the projection light exiting via thesecond face.

(#9) In the optical unit according to any one of (#1) to (#8), there arefurther provided a plurality of fitting portions to which the digitalmicromirror devices are fitted. The fitting portions are disposed so asto correspond to the first prisms respectively, and the digitalmicromirror devices form an image through intensity modulation on theillumination light through ON/OFF control of the inclination of thefaces of a plurality of micromirrors that pivot about a pivot axis.

(#10) In the optical unit according to (#9), the micromirrors each have,as the pivot axis, two mutually perpendicular pivot axes, and thedriving of the individual micromirrors is performed with respect to thetwo pivot axes. The plane that includes the optical axis of theprojection light leaving the first face and that passes through thecenter of one of the digital micromirror devices in its longer-sidedirection and runs parallel to its shorter-side direction isperpendicular to the illumination light reflecting face.

(#11) In the optical unit according to (#10), there are further providedthird prisms disposed between the digital micromirror devices and thefirst prisms respectively. The third prisms each have an OFF-lightreflecting face that transmits, as the projection light, ON-lightreflected from micromirrors in an ON state in the digital micromirrordevices and that reflects, as unnecessary light, OFF-light reflectedfrom micromirrors in an OFF state in the digital micromirror devices.

(#12) In the optical unit according to (#11), conditional formula (1)below is fulfilled:

θ_(OFF)>sin⁻¹(1/n)>θ_(ON)  (1)

where

-   -   θ_(ON) represents the angle of incidence of the ray of the        ON-light with the largest angle of incidence with respect to the        OFF-light reflecting face;    -   θ_(OFF) represents the angle of incidence of the ray of the        OFF-light with the smallest angle of incidence with respect to        the OFF-light reflecting face; and    -   n represents the index of refraction of the third prisms.

(#13) A projector includes an optical unit according to any one of (#9)to (#12); a light source; an illumination optical system that emitsillumination light toward the reflecting member in the optical unit; anda projection optical system that projects onto a screen, on an enlargedscale, the image displayed on the digital micromirror devices fitted tothe fitting portions.

(#14) In the projector of according to (#13), the projection opticalsystem is disposed to face the first face in the optical unit, thereflecting member is disposed below the optical axis of the projectionlight leaving the first face, and the projection optical system ismovable the an up-down direction.

According to the optical unit structured as described above, the opticalaxis of the illumination light striking, as incident light, theillumination light reflecting face and the optical axis of theprojection light on the first face are disposed on the same plane whichis the optical axis plane. A first component vector that is obtained,when a first, outward, normal vector to the first face is projected ontothe optical axis plane, by it being projected to be disposed on the sameside as the optical axis of the incident light with respect to theoptical axis of the projection light points in such a direction that,the farther away from the first face, the farther away from the opticalaxis of the projection light leaving the first face. It is thuspossible, while preventing a drop in the amount of light in theillumination light totally reflected on the illumination lightreflecting face, to increase the distance between the optical axis ofthe projection light near the first face leaving the first face and thereflecting member in the direction perpendicular to the optical axis ofthe projection light. Thus, in a case where the projection opticalsystem is disposed to face the first face in the optical unit, the shiftamount of the projection optical system in the direction toward thereflecting member can be increased. It is thus possible, whilepreventing a drop in the amount of projection light, to enhance theusability of the optical unit and the projector.

Although the disclosure has been described with respect to only alimited number of embodiments, those skilled in the art, having benefitof this disclosure, will appreciate that various other embodiments maybe devised without departing from the scope of the present invention.Accordingly, the scope of the invention should be limited only by theattached claims.

What is claimed is:
 1. An optical unit in which illumination light isdirected to a plurality of digital micromirror devices that produceprojection light by modulating the illumination light on an imagedisplay surface according to an image signal, wherein the optical unitemits the projection light produced by the digital micromirror devices,the optical unit comprising: a reflector having an illumination lightreflecting face on which the illumination light is reflected; and aprism unit composed of a plurality of first prisms, wherein thereflected illumination light enters the prism unit via a first face of amost emergence-side first prism among the first prisms and theprojection light exits via the first face, wherein the reflector isdisposed next to the first face and protrudes from the first face in aprojection light exiting direction, an optical axis of the illuminationlight striking, as incident light, the illumination light reflectingface and an optical axis of the projection light on the first face areon a same plane, wherein the same plane is an optical axis plane, when afirst outward normal vector to the first face is projected onto theoptical axis plane, a first component vector is obtained by the firstoutward normal vector being projected on a same side as the optical axisof the incident light with respect to the optical axis of the projectionlight, and the first component vector points in a direction along whichthe farther away the first component vector is from the first face, thefarther away the first component vector is from the optical axis of theprojection light leaving the first face.
 2. The optical unit accordingto claim 1, wherein at least one of the first prisms has a dichroic coatface, and the prism unit executes color separation for the illuminationlight and color integration for the projection light.
 3. The opticalunit according to claim 1, wherein when a second inward normal vector toan opposite face facing the first face of the first prism is projectedonto the optical axis plane, a second component vector is obtained bythe second inward normal vector being projected on the same side as theoptical axis of the incident light with respect to the optical axis ofthe projection light, and the second component vector points in adirection along which the farther away the second component vector isfrom the opposite face, the farther away the second component vector isfrom the optical axis of the projection light leaving the first face. 4.The optical unit according to claim 1, wherein the illumination lightreflecting face is disposed outside a beam of the projection light. 5.The optical unit according to claim 1, wherein the reflector is aninternal total reflection prism, and the illumination light reflectingface is a total reflection face in the internal total reflection prism.6. The optical unit according to claim 1, wherein the reflector is amirror, and the illumination light reflecting face is a mirror face inthe mirror.
 7. The optical unit according to claim 1, furthercomprising: an emergence-side optic having a second face, wherein theoptical axis of the projection light is in a direction normal to thesecond face, the projection light emerges from the second face, and theemergence-side optic is disposed on a projection light exiting directionside of the first face, wherein a prism unit-side end part of a beam ofthe illumination light on the illumination light reflecting face isdisposed on a same side as the prism unit with respect to the secondface, and an intersection line between the illumination light reflectingface and the second face is outside the beam of the projection light onthe second face.
 8. The optical unit according to claim 7, wherein theemergence-side optic is a second prism, the projection light enters thesecond prism via an entrance face of the second prism facing the firstface, and the projection light exits the second prism via the secondface.
 9. The optical unit according to claim 1, further comprising: aplurality of fitting portions to which the digital micromirror devicesare fitted, wherein the fitting portions are disposed to correspond tothe first prisms respectively, and the digital micromirror devices forman image through intensity modulation on the illumination light throughON/OFF control of inclination of faces of a plurality of micromirrorsthat pivot about a pivot axis.
 10. The optical unit according to claim9, wherein the micromirrors each have, as the pivot axis, two mutuallyperpendicular pivot axes, each of the micromirrors is driven withrespect to the two pivot axes, and a plane perpendicular to theillumination light reflecting face: includes the optical axis of theprojection light leaving the first face, passes through a center of oneof the digital micromirror devices in a longer-side direction, and runsparallel to a shorter-side direction.
 11. The optical unit according toclaim 10, further comprising: third prisms disposed between the digitalmicromirror devices and the first prisms respectively, wherein the thirdprisms each have an OFF-light reflecting face that transmits, as theprojection light, ON-light reflected from the micromirrors in an ONstate in the digital micromirror devices and that reflects, asunnecessary light, OFF-light reflected from the micromirrors in an OFFstate in the digital micromirror devices.
 12. The optical unit accordingto claim 11, wherein conditional formula (1) below is fulfilled:θ_(OFF)>sin⁻¹(1/n)>θ_(ON)  (1) where θ_(ON) represents an angle ofincidence of a ray of the ON-light with a largest angle of incidencewith respect to the OFF-light reflecting face; θ_(OFF) represents anangle of incidence of a ray of the OFF-light with a smallest angle ofincidence with respect to the OFF-light reflecting face; and nrepresents an index of refraction of the third prisms.
 13. A projectorcomprising: the optical unit according to claim 9; a light source; anillumination optical system that emits illumination light toward thereflector in the optical unit; and a projection optical system thatprojects onto a screen, on an enlarged scale, the image displayed on thedigital micromirror devices fitted to the fitting portions.
 14. Theprojector according to claim 13, wherein the projection optical systemis disposed to face the first face in the optical unit, the reflector isdisposed below the optical axis of the projection light leaving thefirst face, and the projection optical system is movable in an up-downdirection.